Power microwave tubes use magnetic flux to emit microwave radiation. The invention has application in magnets for gyrotron, peniotron tubes and other types of high frequency microwave tubes that require very high magnetic fields, such as millimeter and submillimeter wave traveling-wave tubes, backward wave oscillators, carcinotrons, and others. In this application, reference to “power microwave tubes” is intended to be broadly defined to include: (1) high frequency microwave tubes of varying types and interactions; and, (2) microwave generators, especially those that would benefit from higher magnetic fields. Gyrotrons and peniotrons, with their microwave cavities, are used as examples herein, but it should be understood that principles discussed apply the larger spectrum of power microwave tubes as defined above.
A gyrotron gyrates the path of a stream of electrons flowing through a cavity in a strong magnetic field and, by doing so, imparts electrons with cyclotron motion while emitting a millimeter wave beam. Essentially, microwaves are generated by maser effects of cyclotron resonance. A peniotron uses the energy exchange between gyrating electrons and a high frequency electromagnetic field structure to generate microwaves. Gyrotrons and peniotrons are high powered electron tubes that convert electron kinetic energy to microwave radiation using a magnetic field.
High-power microwave tubes above 30 gigahertz frequently employ, and gyrotrons almost exclusively employ, a superconducting magnet system. Major problems with current technology employing a superconducting magnet system reside in the weight of the magnet system and its attendant refrigeration equipment, its contribution to cost and reliability, the continuous power it consumes, and the cool-down time prior to initial operation. Superconducting magnets are expensive and difficult to transport, operate and maintain outside a controlled environment, such as in a laboratory or fixed industrial installation.
The present invention provides (1) a permanent magnet having a magnetic flux density exciting a large air gap; (2) an electromagnet having a magnetic flux density exciting the same large air gap; and, (3) a though-bore for the insertion of a microwave tube through the magnet. The combination under the specified configuration yields a magnetic flux density significantly larger in the large air gap than the air gap flux densities from either magnet operating alone. Under certain conditions, such as when incorporating non-linear magnetic materials, the resultant magnetic field can be even significantly larger than the sum of the fields of the individual magnets. As referred to herein, the air gap is the distance though the air from one pole to the other of a magnet having a through-bore.
This combination of electromagnet or solenoid and permanent magnet in the specified configuration is termed an electropermagnet. The import of the electropermagnet is that it is a very powerful magnet that may be employed in power microwave tubes that exploit an optimum magnetic-field-strength, or cyclotron harmonic number, thus avoiding the need for superconducting electromagnets.
A magnet for a power microwave tube must be extremely stable or the device will be detuned, jump to inefficient modes, or not even work at all. This has been a key problem area for magnets used for power microwave applications. The electropermagnet of the current invention provides a magnet with a highly constant field that is also tunable over a large temperature variation.
In addition, the invention adds versatility in that it provides a high magnetic field when using magnetic materials with either a high coercive force or a low coercive force. The coercive force is the amount of reverse magnetic field which must be applied to a magnetic material to make the magnetic flux return to zero.
The coercive force is a property or type of the material comprising the permanent magnet for which a continuum of high to low coercive force material is possible. The invention applies to the continuum, but is described herein for convenience and to facilitate description of the invention in terms of high-coercive force or low-coercive force materials. For both of these types of materials, the invention also yields desirable characteristics of higher temperature tolerance, ruggedness, and lower cost.
The present invention helps to solve the above-identified problems by eliminating the need for a superconducting magnet system in power microwave tubes.